First of all, hi, I'm a big fan of your comments and you seem to be the most active user on this site (Also, your username always gets a chuckle out of me. Sí, sé lo que significa garompa, hahaha)
Uhm, what you had to do when you got to the pillars was moving the one that was moveable to the red grids in the leftmost room of the first floor (the one that isn't where you found the "hornet gun"). When you place that one, you can move the other one and place it in the other red grid. After that, the assasins spawn… And then, when you kill them all, well, I got stuck there, since I walk over the floating map and just go through it.